1. Field of the Invention
The present invention relates to a double admitting pressure intensifier where the pressure intensifier piston is automatically controlled and reversed in the end positions by a control slider, which control slider is disposed in parallel to the pressure intensifier piston.
2. Brief Description of the Background of the Invention Including Prior Art
Pressure intensifiers have been proposed where the reversal of the direction of motion of the pressure intensifier piston is provided by a control shell surrounding the pressure intensifier piston or by a control slider disposed for running in parallel to the pressure intensifier piston. According to one embodiment with a control shell, this is in most cases shifted mechanically by way of stops of the pressure intensifier piston when approaching its end position and thus the admission stroke of the pressure intensifier piston is controlled. Since the mechanical control of the control shell does not result in a stable control despite corresponding auxiliary steps in the end positions, a hydraulic control has been created. According to the hydraulic control, the annular surface of two bands at the outer diameter of the control shell or front faces at the ends of this control shell are connected alternatingly depending on the position of the pressure intensifier piston to the pressure or the discharge side. The adjustment motion of the control shell in that case always runs against the direction of motion of the pressure intensifier piston. The control bores cut in the control shell are rapidly and completely released by the opposite motion relative to the pressure intensifier piston, whereby the control shell is shifted alternatingly in each case into a different position such that a stable reversal of the direction of motion of the pressure intensifier piston is provided under any conditions, for example if a large or a small transported flow or, respectively, pressure is present. The safe control and direction reversal of the pressure intensifier piston thus is associated with a geometrical coordination of the pressure intensifier piston to the control shell and this appears to be possible only if the pressure intensifier piston and the control shell are touching or, respectively, if the pressure intensifier piston is surrounded by the control shell. This coaxial coordination of the pressure intensifier piston and of the control shell, in particular if the latter is surrounded by three further control bushings, is disadvantageous from a production, manufacturing point of view. Small deviations from coaxiality result in a clamping of the control shell if the gaps and thus the leakage losses are to be kept to a small value.
Therefore, an embodiment with a control slider running parallel to the pressure intensifier piston has been proposed. The control slider is provided with two flat control grooves in its middle part.
The bore for the pressure intensifier piston is connected via a control bore to a feed line and on either side of this control bore and at a certain distance from it, is connected by a control bore to the discharge port. Two closely neighboring bores are disposed on each side in between and somewhat staggered relative to the side bores, which bores connect the bore of the control slider to the pressure intensifier piston.
The pressure intensifier piston is provided with two inner, somewhat broader, flat and two outer, somewhat narrower control grooves which release and open or, respectively, cover the mentioned control bores. The proposed pressure intensifier however does not work satisfactorily under all operating conditions. In particular, difficulties occur if in the case of a high counter pressure, the primary stream goes to zero because the primary pressure limiting valve is engaged. Then the control slider becomes stuck in the middle position. Several causes exist for this situation. The main cause is that a pressure pulse is exerted on the control slider by the control grooves during the lift stroke of the pressure intensifier piston. Since the neighboring bores in the casing are closely spaced in the axial direction relative to each other, their operation activity is eliminated by the loss of the gap.